JPS6358211A - Optical displacement detecting device - Google Patents

Abstract

PURPOSE:To improve the resolution and accuracy of displacement detection by processing transmitted light beams of a main scale and an index scale which have plural relatively movable arrays of optical gratings as specified and detecting the absolute value of the quantity of relative movement. CONSTITUTION:This detector consists of the main scale 10 with two arrays of optical gratings 13 and 15 differing in pitch and the opposite index scale 20 with two arrays of reference optical gratings 23A and 25A differing in pitch. When the scale 20 is moved relatively, electric signals which have a phase difference theta1 are outputted by photoelectric elements 33A and 33B corresponding to one array of gratings having a 90 deg. phase shift and signals which have a phase difference theta2 are outputted by elements 35A and 35B corresponding to the 2nd array of gratings. An absolute displacement detecting circuit 50 samples and holds the signals and also computes theta2-theta1 to find the absolute value of the quantity of relative movement between the scales 10 and 20. Consequently, the displacement detection is performed with high resolution and high accuracy.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to an optical system having a relatively movable optical grating and detecting relative f-hyperactivity by processing transmitted light or reflected light from the optical grating in a predetermined manner. The present invention relates to a type displacement detection device, and in particular, is capable of detecting an absolute displacement amount by providing a plurality of rows of optical gratings.

[Background technology and its problems]

It is known to detect the relative displacement between independent objects to determine physical specifications (length, pressure, weight). As one of the means for this purpose, optical displacement detection devices are widely used.

Conventionally, such a general transmission type optical displacement detection device has a structure shown in No. 617I.

That is, the main scale 10 having the optical gratings 13 aligned in the longitudinal direction and the index scale 20 having the corresponding reference optical gratings 3A and 3B are connected to each other of two objects (for example, a stationary body and a movable body) facing each other. Attach it to
Light source 1 and photoelectric converter 2A and 2B are connected to both scales 10
．． A signal detection circuit 7 is disposed integrally with the index scale 20 with 20 in between, and selectively includes a waveform shaping circuit, a dividing circuit, a direction discrimination circuit, etc. for processing the output signals from both photoelectric converters 2A and 2B. , a reversible counting counter 8, and a display means 9 consisting of a digital display or the like.

Therefore, the arrow X
If relative movement is made in the direction, both optical gratings 13.3A, 3B
The transmitted light that has passed i3 is transmitted through photoelectric converters 2A and 2B.
By performing predetermined processing in the signal detection circuit 7, for example, 1
It was possible to count the digital signal of μml pulses with the counter 8, display the amount of displacement on the display means 9, and further output an electric signal corresponding to the amount of displacement to other equipment. In addition, 2
The reason why the two photoelectric converters 2A and 2B are provided is to provide a direction discrimination function, and also to enable them to be used to double the resolution depending on the division method.

However, the conventional optical displacement detection device described above has the following problems.

First, since it is an incremental method, it is difficult to operate in an absolute manner.

That is, the photoelectric converter 2A.

The output of 2B is, for example, the slit width of the optical grating 13 by 1
This is because if the five pitches of 0 μm are set to 20 μm, a cyclic signal having a substantially sinusoidal waveform with one cycle of 20 μm of one mouthpiece length will be obtained. Therefore, T added to the main scale 10
A quasi-absolute method is used in which an S magnetic switch is installed to determine the so-called absolute origin, but this does not change the incremental method within the interval between the El'r1m switches, so this is a fundamental solution. Not only does it not work, but it also becomes larger due to the provision of the IM switch, etc.
There were problems of increased economic burden and lack of credibility.

On the other hand, an absolute type detection device in which the main scale 10 is provided with a binary coat, a gray code, etc. is also considered, but this type would inevitably increase the size of the equipment, and would not be accurate enough to satisfy the current high precision requirements. It has a fundamental drawback in that resolution cannot be obtained, making it difficult to use in industry.

Second, since it is an incremental method, there are inherent problems such as unstable accuracy or accuracy guarantee. If there is even one erroneous count due to noise etc. during measurement, the value displayed on the display means 9 during the process, that is, the measured value, becomes meaningless, and the erroneous count is not easily noticed due to the high resolution. This had the fatal drawback of not being able to avoid product defects.

As a result, not only strict noise countermeasures are required and the equipment becomes too large, but also there is a problem that the manner of use is restricted because it is not a complete countermeasure.

Thirdly, there were disadvantages and inconveniences in terms of use and handling.

That is, while the table feed speed of the machine tool is a matter of arbitrary selection by the user, the displacement detection device has a limit on the permissible relative movement speed of both scales of 10° and 20°, which is determined by the characteristics of the electrical component. Therefore, there is a problem in that the response speed is limited in that if the relative movement speed is used at a high speed exceeding the allowable relative movement speed, erroneous counting will occur. Furthermore, if the power to the device is cut off due to operation on the user's side or by accident or carelessness, the cumulative count value will be lost, and the work efficiency will be lowered as the cumulative count value will be lost. there were. On the other hand, in order to avoid this, a bank-up power supply had to be provided, which was a problem in terms of equipment economics.

These problems are due to the fact that conventional optical displacement detection devices are incremental in structure. development was strongly desired.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-mentioned conventional problems and provide an absolute type optical displacement detection Ia jiff which is considered to be a slip S and has high resolution, high precision, and a wide detection range.

[Means and effects for solving the problems] The present invention has the following features:
The main scale is equipped with multiple rows of optical gratings with different pitches and recesses for each row, and the index scale is also equipped with optical gratings with corresponding rows and corresponding pinches, and electrical signals are output by engaging with each of the multiple rows of optical gratings. By skillfully utilizing the phase difference between the two scales, it is possible to detect the absolute displacement of the relative movement of both scales over a wide range significantly larger than the pinch of the optical grating with a resolution smaller than the pitch of the optical grating. It is something.

Therefore, a plurality of rows of optical gratings are provided; a main scale in which each row has a different optical grating pitch, and a plurality of rows of reference optics corresponding to each row of optical elements of the main scale. an index scale provided with a grating and movable relative to the main scale; a parallel illumination system for irradiating both scales with parallel light; and two sets of optical gratings arranged for each row of optical gratings of the main scale A plurality of sets of photoelectric converters are installed, and each set receives the transmitted light transmitted through the main scale or the reflected light reflected from the main scale, and outputs electricity (No. 3) with a 90 degree phase. Then, find the inter-set phase difference between the electrical signals output from each set of the photoelectric converters, and use this inter-set phase difference to calculate the absolute value of the relative movement displacement between the main scale and the index scale. The above object is achieved by a configuration including an absolute displacement detection circuit formed so as to be able to detect the displacement.

Therefore, if the main scale, which is provided with a plurality of rows of optical gratings with different pinches, and the index scale, which is provided with a plurality of corresponding rows of reference optical gratings with different pitches, are moved relative to each other in the longitudinal direction, for example, In the case of two rows of optical gratings, one set of two pieces with a phase shift of 90 degrees is used.
The photoelectric converter corresponding to the reference optical grating in the row outputs an electrical signal with a phase difference θ1, and similarly, the photoelectric converter corresponding to the reference optical grating in the second row outputs an electrical signal with a phase difference θ2. A signal is output.

Here, the absolute displacement detection circuit samples and holds the electrical signal with the phase difference θ and the electrical signal with the phase difference θ2 at appropriate times, calculates the inter-group phase difference (θ2-θ1), and calculates the inter-group phase difference ( θ2-01) can be used to find the absolute value of the relative movement amount of both scales.

〔Example〕

An embodiment of the optical displacement detection device of the present invention will be described in detail with reference to the drawings.

This embodiment is shown in FIGS. 1 to 4, and the apparatus includes a main scale 10 provided with a plurality of rows (two rows) of optical gratings and an index scale 20 provided with a corresponding reference optical grating. A parallel illumination system 40 for irradiating both scales 10.20 with light, a plurality of Mi (2jli) photoelectric converters 30 that receive passing light from both scales 10.20 and output electrical signals, and Both scales 1 to find the difference
and an absolute displacement detection circuit 50 formed to be able to detect the absolute value of the relative displacement amount of 0.20.

The main scale 10 is in the form of an elongated thin plate made of a glass material 11 with a rectangular cross section, as shown in the second part of FIG. Pitch P on the side! (=P-ΔP) is 398
A second optical grating 15 with a diameter of 1 m is provided.

Here, the first optical grating 13 has a detection range of 80 mm)
Since it is formed to divide into N (=200) equal parts and the second optical grating 15 into N+1 equal parts, L=NP= (N+1)(P-ΔP)...(1
) holds true. The above values were chosen for this relationship.

On the other hand, the index scale 20 is the main scale I.
A first reference optical grating 23A (corresponding to the first optical grating 13 of the main scale 10) is provided on the lower side as shown in FIG. 23B) and a second optical grating 15 on the upper side.
A second reference optical grating 25A (25B) corresponding to the second reference optical grating 25A (25B) is provided.

The pitch of the first reference optical grating 23A (23B) is q, the pitch of the second reference optical grating 25A (25B) is q-Δq, and the corresponding first and second optical gratings in the longitudinal direction are Two sets of reference optical gratings 23A, 23B, 25A, 2 whose phase is shifted by 90 degrees with respect to the optical grating 13°15
5B is provided. Note that in this example, q=p,
It is assumed that Δq=ΔP.

Next, the photoelectric converter 30 has four photoelectric elements 33A forming two sides (30A, 30B).

33B, 35A, and 35B, and are arranged correspondingly to each reference optical grating 23A, 23B, 25A, and 25B, and preamplifiers 37A, 37B, 38A, and 38B are connected to each photoelectric element 33A, 33B, 35A, and 35B, respectively. has been done. Furthermore, on the opposite side of the photoelectric converter 3o with both scales 10.20 in between, a parallel illumination system 40 is provided to irradiate parallel light onto both scales 10.20, which is composed of a light source 41 consisting of an LED and a collimator lens 42. The parallel illumination system 40 has a predetermined relationship with the index scale 2o and the photoelectric converter 30, and can be moved integrally with the main scale 10 in the X direction in the figure.

Here, as seen in FIG. 2, the point T where the first optical grating 13 and the second optical grating 15 coincide is set as the origin, and the coordinates, that is, the index scale relative to the main scale 10, are set in the right direction in the figure. Letting the relative movement displacement amount of 20 be X,
The photoelectric elements 33A and 33B are the first reference optical grating 23A.
, 23B with a phase difference of 90 degrees, the output of the photoelectric element 33A is a+, the photoelectric element 33
If the output of B is bl, both optical elements 33A and 33B
The phase difference θ1 of the electrical signal from the origin can be approximated as . Note that □ in the second term on the right side of equation (3) is introduced as a correction term because the amount of transmitted light is maximum at the origin T.

Similarly, the outputs of the photoelectric elements 35A and 35B are respectively aZ
+bt, the phase difference θ2 between the electrical signals from the photoelectric elements 35A and 35B can be approximated as follows.

Further, the absolute displacement detection circuit 50 detects the relative movement displacement 1 of both scales 10 and 20 from the touch sensor 65 via the CPU 55.
Depending on the trigger that is output when trying to find x,
Each photoelectric element 33A, 33B.

Output signals of 35A and 35B al r bI + a
A sample and hold circuit 51 for sampling and holding t r b2 and the output signal al + bI + held from this sample and hold circuit 51
Multiplexer 5 that sequentially takes out one of 32 +b2
2, an A/D converter 53 that converts the analog output signal extracted by the multiplexer 52 into a digital signal, and the sample and hold circuit 51, the multiplexer 52, and the A/D converter 53 via the control data bus 54.
The CPU 55 is configured to provide timely commands, etc. to the CPU 55, and perform predetermined arithmetic processing, etc. described below based on the input data. It is connected.

Now, in the CPU 55, as shown in FIG. 4 (B), finally X=X, +ΔX,=np+ΔX t ”'
The absolute displacement meter X from the origin T is determined as e.

Note that the vertical axis of FIG. 4(B) is set to θ1−□ in relation to the 2nd term on the right side of equation (3). , : Here, X is the wide range displacement amount in the first optical grating 13 of the main scale 10, and is the number n of pitches P that are 1ffi apart from the pitch P of the first optical grating 13 (n is 1 or more). ΔX+ is the absolute displacement amount of the first optical grating 13 within the fi+1st pinch P.

That is, the present invention provides a plurality of rows (two rows in this embodiment) of optical gratings 13.15 on the main scale 10, and each set of photoelectric elements 35B, 3 corresponding to each optical grating 13.15.
The reason why the absolute system was adopted by utilizing the inter-set phase difference (.theta.2-.theta.) between 5A, 33B, and 33A is as follows.

That is, the above equation (5) can be converted as follows.

P-ΔP1... (7) Then, substituting equations (3) and (2) into equation (7), tX = -(θ2-θ,)... (9)
2 π.

Therefore, in the CPU 55, from equation (9), the photoelectric element 33A corresponding to the first optical grating 13 of the main scale lO,
Phase difference θ1 of output signal aI+bI from 33B
and photoelectric elements 35A, 35 corresponding to the second optical grating 15
Outgoing signal a from B! If the phase difference θ2 of +b2 is determined, the absolute displacement 1x from the origin T can be determined since the length of the detection range has been determined.

Here, θ and θ2 are obtained from equations (4) and (6)...
... It is demanded as a cry.

Furthermore, in this example, in order to further stabilize the accuracy, θ
Rather than making 1 and 02 independent, they are formed to have a correlation function to determine the absolute displacement X.

If θ2 and 01 were obtained independently and simply subtracted based on equation (9), each photoelectric element 33A, 33B, 35
A, output signals from 35B al+bl+a2. b2
is the p+P of each optical grating 13.15.

This is because the waveform is cyclic for each P-ΔP, so there is a risk of loss of digits.

Therefore, a and b are newly defined.

By substituting the formula (21, (41) into this 80υ, a=AB
sin(02-〇I) b=ABcos(θ2- θI) --tan (θ2- θ1) ・・
・・・・・・ Because it hits, θ2−θ+ = tar+−' □・・・・
... Assuming that the value is 0, the photoelectric element 35A is calculated by calculating the arctangent function.

The phase difference (θ) between the strings 35B, 33A, and 33B.

-θ1).

By the way, as is clear from 203, the phase difference between the pairs (θ2
-θI) changes from θ to 2π within the detection range length as seen in No. 21 (A), so the displacement to point Q in the figure: (° is the absolute value of X shown in (B)). This is an approximate value. Therefore, similarly to equation (9), ■ holds true.

Furthermore, as shown in Fig. 4 (B), the absolute value X of the relative movement amount of both scales 10.20 must be determined as the wide range displacement Xl and the narrow range displacement ΔX (2Q61 reference).

Here, from equation (31, Qω), the first of main scale 10
Although it is possible to determine the narrow range displacement ΔX of the optical grating 13 within the pinch P, the phase difference θ1 based on the first optical grating 13, the first reference optical gratings 23A, 23B, and the photoelectric elements 33A, 33B Since is a periodic function of the pitch P, it is impossible to specify which pitch (counting from the origin T) it falls within.

Therefore, by converting the phase difference θ, into a value θ1゛ with a phase shift of □ or more to (2π+□) or less, and setting it analogously to equation (3), the following holds true.

On the other hand, the number n of pitches P of the first optical grating 13 that has passed from the origin T to the relevant point in time is expressed as
It is clear that the number does not exceed P and is an integer.

However, as an exception, in Figure 4, the measurement resolution Δ
In the case where L is the same as (B) and includes a region where the phase changes to 2π-0, and ΔX is 2π, it is sufficient to add 1 to the integer to O.

Here, as shown in the formula Oa, was asked for.

Therefore, it can be determined as a function of n=f (θ2-θ1.8Xt).

From the above, in cpus s, X = np + ΔX of the formula QQ
By calculating , it is possible to obtain the absolute (+i!

Next, the operation of this embodiment will be explained.

For example, main scale 1 is installed on a stationary object such as a machine tool vent.
0 is fixed, the index scale 20 is integrated with the parallel illumination system 40 and the photoelectric converter 30, and the index scale 20 is fixed to a movable body such as a slider. Therefore, when the main scale 10 and the index scale 20 move relative to each other by operating the machine tool, each photoelectric element 33A, 33B, 35A
, 35B generates a substantially sinusoidal electrical signal al+ bl+
aZ+bt is output, signals al+ bl and 32
+bZ, the cycle is different from the one corresponding to the pinch difference of the optical grating 13.15, and the signal a, and a2
and b2 each produce a phase difference of 90 degrees.

Here, as shown in FIG. 3, a touch sensor 65 is activated when it is desired to display the absolute value of the relative displacement amount of both scales 10° 20 on the display means 60 or output it as a feedback signal to a control device (not shown). When a trigger is input from the CPU 55 (step 10), a hold command is issued from the CPU 55 to the sample hold circuit 51 via the control data bus 54.

The sample hold circuit 51 is a preamplifier 37A.

Analog electrical signals al+t)1 and 22+bt are held from the output stage side of 37B, 38A, and 38B (step 12).

Next, as in step 14, the multilexer 52
Electrical signal a based on the command from 55.

, b, and at+ b2, and A/D converter 53
After converting the signal into a digital signal, the signal is input to the CPU 55.

Hereinafter, the CPU 55 selects the photoelectric element 33A corresponding to the first optical grating 13 based on the formulas 〇l and α9.

33B and the narrow range displacement amount ΔX are calculated (step 16), that is, the displacement amount of the first optical grating 13 within the pitch P is determined as an absolute value. Of course, the phase difference θ is converted within the C2U55 to θ1゛, which is a value of □ or more to (2π+□) or less, in order to specify which pinch is within.

In addition, in step 18, the definition signals a and b based on 2aυ, 03 and the photoelectric elements 35Δ, 35B and 33A are
, 33B, the inter-group phase difference θ2−θ1 based on each phase difference with
, and calculate the arctangent function to obtain the phase difference θ between the pairs.
2-θ1 is calculated.

Now, based on n=f (θ2-θ1.ΔXI), the number n of pinches P of the first optical grating 13 that has passed so far, which corresponds to FIG. 4, is determined (step 20).

Therefore, in step 22, the absolute value X of the relative displacement amount of both scales 10.20 is determined by calculating 2〇〇. This absolute value X is displayed on the display means 60,
Output to the outside as necessary. Here, the absolute displacement amount at a desired time point specified by the touch sensor 65 can be detected and displayed.

In this example, the pitch P of the first optical grating 13 of the main scale 1o is 400 μm, and the relationship between the first optical grating 13 and the second optical grating 15 is the detection range length L = 80.
Since it is defined as 1 and N=200, the absolute value can be detected within the detection range length (L=8 omws) with a resolution of 2 μm.

Therefore, according to this embodiment, the main scale 10 is provided with a plurality of rows of optical gratings (13, 15) each having a different pinch (P, P-ΔP), and these optical gratings (13, 15)
) The relative movement displacement amount between the main scale 10 and the index scale 20 can be detected as an absolute value within the detection range length (L) using the inter-set phase difference (θ2 - θ1) found from the relationship between . Since an absolute type optical displacement detection device can be established here, industrial applicability can be dramatically expanded in terms of accuracy and operational technology.

This ensures stable predetermined accuracy because there is no influence of noise on the way and there is no accumulation of noise, and since continuous tracking is not required, response speed is high and rapid measurement can be achieved. This means that even if the power is cut off, it is possible to immediately re-measure without having to adjust the origin each time, thereby eliminating the drawbacks, disadvantages, and inconveniences of the conventional incremental method.

In addition, multiple rows of optical gratings (
13, 15) is physically fixed on a glass plate by an etching method, etc., and uses the inter-group phase difference between optical gratings of different pinches and the phase difference within the two optical gratings. Since the system is designed to detect the absolute value of the amount of displacement, for example, unlike the case where the waveform generated in an I-pinch is electrically subdivided by splitting the I-pinch in a conventional incremental system, both scales can be detected. 10.20, that is, it is compatible with the machine tool to be adopted, so true high-precision measurement can be guaranteed.

Furthermore, in order to obtain the phase difference between the two optical gratings 13.15, the phase difference between the two optical gratings 13. By establishing a close and inseparable correlation with , it is possible to perform detection without any deviation. High accuracy is guaranteed from this point as well.

In this example, the pitch P of the first optical grating i3 of the main scale lO is 400 μm, the pitch P−ΔP of the second optical grating 15 is 398 μm, and the range of the detection range length L (80 m−) 2 with the number of divisions N being 200 within
Although it was formed so that it can be detected with a resolution of μm, these numerical items can be arbitrarily selected, and the resolution is 0.1.
It can also be less than μm. In this sense, the main scale 10 is provided with two rows of optical gratings 13, 15, but the same can be done with three or more rows. If there are three or more rows, the length of the detection range can be selected widely and variously.

Similarly, reference optical grating 35 of index scale 20
For A and 35B, the pitch q is the same as the pinch of the first optical grating 13 of the main scale 10, but the pitch is 1/n (n is an integer of 1 or more) with respect to the pitch P1 of the corresponding optical grating.
The present invention is also applicable in the case where the optical grating 13, 15 of the main scale 10 is loaded with resolution without modification. In addition, each reference optical grating 23A, 23
B, 25A, and 25B were formed from two pieces each with a phase shift of 90 degrees, but the point is that the corresponding main scale 10
Optical grating 13. If it is possible to generate a phase difference in relation to i5, each 1
It can also be formed individually. Furthermore, by arranging optical gratings 15 above and below optical grating 13 and averaging the upper and lower phase differences, it is also possible to correct the tilt of index scale 20 with respect to main scale lO.

Further, although the detection device itself is a transmission type using a parallel illumination system, it may be a reflection type as shown in FIG. 5, and the present invention is also applicable to a rotary type instead of a linear type. Also,
Although the touch sensor 65 is used to specify the time of displacement detection, the present invention is not limited to this, and the absolute displacement detection circuit 50 may be configured to detect displacement at every fixed sampling time.

Furthermore, the detection range length is the length in the direction of relative movement between the main scale 10 and the index scale 20, but since this detection device detects displacement, the measurement target is limited to length, width, etc. Instead, it may be pressure, weight, etc.

Of course, compared to the case where the absolute method is implemented using a binary code or Gray code for the main scale, the number of grid rows can be significantly reduced, the pitch can be made narrower, and the dynamic range (
It is understood that the detection range/resolution) is high, and there is a significant difference in its practical value. Furthermore, ill! has a long detection range! It is also easy to count excessive points and perform extended detection over multiple detection range lengths.

〔Effect of the invention〕

The present invention has the advantage of being able to provide an absolute optical displacement detection device with high quantitative resolution, high precision, and a wide detection range.

[Brief explanation of drawings]

FIG. 1 is an overall configuration diagram showing an embodiment of the optical displacement detection device according to the present invention, FIG. 2 is an enlarged view of the main parts, and FIG. 3 is a flowchart for calculating the absolute displacement amount. 4 is a waveform explanatory diagram, 5th [12I is a main diagram 4F1 showing another embodiment, and FIG. 6 is a schematic configuration diagram of a conventional optical displacement detection device. DESCRIPTION OF SYMBOLS 10... Main scale, 13... First optical grating, 15... Second optical grating, 20... Index scale, 23... First reference optical grating, 25...
Second reference optical grating, 30...Photoelectric converter, 40...
- Parallel illumination system, 50...absolute displacement detection circuit.

Claims (4)

[Claims] (1) A main scale provided with a plurality of rows of optical gratings and each row having a different optical grating pitch, and a plurality of reference optical gratings corresponding to each row of optical gratings of the main scale. an index scale disposed and movable relative to the main scale; a parallel illumination system for irradiating parallel light to both scales; and a set of two index scales arranged for each row of optical gratings of the main scale. , a plurality of sets of photoelectric converters each receiving transmitted light transmitted through the main scale or reflected light reflected from the main scale and outputting electrical signals having a phase shift of 90 degrees; and the photoelectric converter. The scale is formed so as to obtain an inter-set phase difference between the electrical signals output from each set, and to detect the absolute value of the relative movement displacement between the main scale and the index scale using this inter-set phase difference. An optical displacement detection device comprising an absolute displacement detection circuit. (2) In claim 1, each reference optical grating of the index scale has an optical grating pitch of P_1, P_2, . . . for each column of the main scale.
When 1/n of the optical grating pitch (n=1, 2,
3,...) corresponding to the optical grating pitch of the main scale. (3) In claim 1 or 2, the absolute displacement detection circuit comprises a wide range displacement amount ( X_L) and one of the optical gratings obtained by using as a variable the electric signal output from the photoelectric converter of the group corresponding to the optical grating of any one column of the main scale.
An optical displacement detection device configured to be able to detect as the sum of the narrow range displacement amount (ΔX_L) within the pitch. (4) In any one of claims 1 to 3, the absolute displacement detection circuit determines the inter-group phase difference as a value obtained from electrical signals output from two sets of the photoelectric converters. is a tangent function of the inter-group phase difference, and the optical displacement detection device is configured to perform calculation by calculating an arctangent of this tangent function.